1. Technical Field
The present invention generally relates to biomedical devices, and especially ophthalmic devices that are intended for direct placement on or in the eye such as contact lenses or intraocular lenses.
2. Description of Related Art
In the field of biomedical devices such as contact lenses, various physical and chemical properties such as, for example, oxygen permeability, wettability, material strength and stability, must be carefully balanced in order to provide a useable contact lens. For example, since the cornea receives its oxygen supply exclusively from contact with the atmosphere, good oxygen permeability is a critical characteristic for any contact lens material. Wettability also is important in that, if the lens is not sufficiently wettable, it does not remain lubricated and therefore cannot be worn comfortably in the eye. Accordingly, the optimum contact lens would have at least both excellent oxygen permeability and excellent tear fluid wettability.
Contact lenses made from fluorinated materials have been investigated for a number of years. Such materials can generally be subdivided into two major classes, namely hydrogels and non-hydrogels. Hydrogels can absorb and retain water in an equilibrium state whereas non-hydrogels do not absorb appreciable amounts of water. Regardless of their water content, both hydrogel and non-hydrogel fluorinated contact lenses tend to have relatively hydrophobic, non-wettable surfaces.
By introducing fluorine-containing groups into contact lens polymers, the oxygen permeability can be significantly increased. For example, U.S. Pat. No. 4,996,275 discloses using a mixture of comonomers including the fluorinated compound bis(1,1,1,3,3,3-hexafluoro-2-propyl)itaconate in combination with organosiloxane components. Fluorinating certain polysiloxane materials has been indicated to reduce the accumulation of deposits on contact lenses made from such materials. See, for example, U.S. Pat. Nos. 4,440,918; 4,954,587; 4,990,582; 5,010,141 and 5,079,319. However, fluorinated polymers can suffer from one or more of the following drawbacks: difficult and/or expensive synthetic routes, poor processability, low refractive index, poor wettability, poor optical clarity, poor miscibility with other monomers/reagents and toxicity.
Another example of introducing fluorine-containing groups into contact lens polymers is U.S. Pat. No. 4,650,843 which discloses a soft contact lens obtained by subjecting, to casting polymerization, a composition containing (a) 50 to 95% by weight of a monomethacrylate of an alkylene glycol, (b) 5 to 35% by weight of a fluorine containing monomer, and (c) 0.3 to 40% by weight of one or more compound selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, glyceryl methacrylate, monomethacrylate of pentaerythritol and an alkyl methacrylate.
U.S. Pat. No. 5,162,469 discloses a one pot synthesis for making contact lenses. The '469 patent further discloses that the contact lenses are obtained from a copolymer containing, by weight, from about 5 to about 85 percent of a polymerizable fluoromonomer, and from about 5 to about 75 percent of a polymerizable hydrolyzable silicone monomer. The copolymer can further include glyceryl methacrylate.
Glyceryl methacrylate is a hydrophilic monomer capable of absorbing a high amount of water and form high water content hydrogels when cured and hydrated. However, glyceryl methacrylate is not very compatible with monomers such as silicone-containing monomers when polymerizing glyceryl methacrylate with the silicone-containing monomer to form a silicone hydrogel. Accordingly, it would be desirable to provide improved biomedical devices using glyceryl methacrylate that exhibit suitable physical properties, e.g., modulus and tear strength, and chemical properties, e.g., oxygen permeability and wettability, for prolonged contact with the body while also being biocompatible.